Theories of internalization typically suggest that self-perceptions of the "causes" of (i.e. reasons for) behavior are differentiated along a continuum of autonomy that contains identifiable gradations. A model of perceived locus of causality (PLOC) is developed, using children's self-reported reasons for acting. In Project 1, external, introjected, identified, and intrinsic types of reasons for achievement-related behaviors are shown to conform to a simplex-like (ordered correlation) structure in four samples. These reason categories are then related to existing measures of PLOC and to motivation. A second project examines 3 reason categories (external, introject, and identification) within the domain of prosocial behavior. Relations with measures of empathy, moral judgement and positive interpersonal relatedness are presented. Finally, the proposed model and conceptualization of PLOC are discussed with regard to intrapersonal versus interpersonal perception, internalization, cause-reason distinctions, and the significance of perceived autonomy in human behavior.